On this day, 117 years ago, July 10, 1908 (June 12, 1908 in the lunar calendar), Dutch physicist Agnes liquefied the last permanent gas helium for the first time. Kamelin? Kamerlingh Onnes was a cryogenic physicist who was born on September 21, 1853 in Groningen, the Netherlands, and died on February 21, 1926 in Leiden, the Netherlands. He won the Nobel Prize in Physics in 1913 for making liquid helium and discovering superconductivity. In 1882, at the age of 29, Onnes was appointed professor of physics and head of the physics laboratory at Leiden University. At that time, physics was in an era of transformation, and people paid more and more attention to physical experiments. After serving as the head of the Physics Laboratory at Leiden University, Onnes decided to focus on studying low-temperature physics. Influenced by van der Waals 'work, Onnes studied the general thermodynamic properties of liquids and gases over a wide range of pressures and temperatures. In order to experimentally support van der Waals's gas theory, especially the "law of corresponding states," Onnes managed to expand the measurement range to the lowest possible temperature. Experiments have found that in order to liquefy the gas, it is necessary to compress the gas and cool it below the critical temperature. If gas is allowed to push the piston to do work externally, or by expanding into vacuum, further cooling will occur, resulting in the liquefaction of some of the gas. In order to achieve low temperatures, the sample must be allowed to exothermic. The most convenient way is to immerse the sample in a liquefied gas. When the liquefied gas vaporizes, the sample will continue to release heat. In order to liquefy refractory helium, Onnes carefully designed a system. A liquid hydrogen evaporation jacket is used to cool the helium, which is then throttled and expanded to liquefy part of the helium. To conduct experiments on low temperatures, we must first obtain low temperatures. Low temperatures are obtained by liquefied gases. Only hydrogen and helium had not yet been liquefied. British physicist Dewar began research in 1877. After more than 20 years, he liquefied hydrogen in 1898. In order to meet the needs of low-temperature research, the Physics Laboratory of Leiden University led by Onnes built a large-scale factory for liquefying oxygen, nitrogen and air from 1892 to 1894. In 1906, it was able to produce large quantities of liquid hydrogen, laying a solid foundation for liquefying helium. After two years of struggle, helium was finally successfully liquefied on July 10, 1908. Created conditions for studying the properties of matter at liquid helium temperatures. Speaking of the unforgettable day when helium was liquefied in 1908, Agnes said: "I was so happy when I presented liquid helium to my friend Van der Waals. It was his theory that guided me until the final victory." The resistance of metals is an important research topic for Onnes. At that time, there were different opinions on how the resistance of metals changed near absolute zero. Some people believed that the resistance of pure metals should gradually decrease with the decrease of temperature and eventually disappear at absolute zero. Onnes originally believed in another idea put forward by Kelvin in 1902, that is, as the temperature decreases, the resistance of a metal reaches a minimum and becomes infinite due to the condensation of electrons on the metal atoms. Because Onnes mastered the technology of liquefying helium, he was equipped to experimentally study this problem. In February 1911, he measured the resistance of gold and platinum at liquid helium temperatures and found that below 4.3K, the resistance of platinum remained constant. Rather than passing a minimum and then increasing it. So he changed his original view and believed that the resistance of pure platinum should disappear at the temperature of liquid helium. To test his opinion, mercury was chosen as the experimental subject because mercury is easier to purify than other metals. The experimental results showed an unexpected and strange phenomenon: the resistance of mercury suddenly disappeared at around 4.2K. This extraordinary discovery not only predicts that power generation efficiency can be greatly improved in the power industry, but also opens up a vast world for people to use this superconductivity to manufacture superconducting motors, superconducting magnets and superconducting cables. From April to November 1911, Onnes reported his experimental results in detail in three consecutive papers. In 1913, Onnes discovered that tin and lead also have the same superconductivity as mercury, and impure mercury also has superconductivity. For his research on the low-temperature properties of matter and the preparation of liquid helium, Heike Kamerlingh Onnes (1853 - 1926) was awarded the 1913 Nobel Prize in Physics. Thanks to Onnes's outstanding leadership and management of the Physics Laboratory at Leiden University, the laboratory became the world's center for cryogenic research at the beginning of this century.